There is a known internal combustion engine which is equipped with in-cylinder injection injectors for directly injecting fuel into cylinders and intake passage injection injectors for injecting fuel into intake passages (including an intake port) and which is configured to select fuel injection from both of the injectors in accordance with the rotation speed and load of the internal combustion engine. The fuel supplied to the intake passage injection injectors is supplied by an electric low-pressure pump provided in a fuel tank. The fuel supplied to the in-cylinder injection injectors is pressurized by a mechanical high-pressure pump mounted on the internal combustion engine and then supplied to the in-cylinder injection injectors.
The mechanical high-pressure pump comprises a plunger that slides within a cylinder by a cam to increase the pressure of the fuel (fuel pressure) in the cylinder, and an electromagnetic spill value that opens and closes a fuel inlet of the cylinder to control a discharge amount to be commensurate with the fuel injection amount of the in-cylinder injectors. This electromagnetic spill valve comprises a spring member for adding a spring force which biases a valve element to an open position, and a solenoid for operating the valve element in a closing direction when being excited.
The electromagnetic spill valve is configured to open the valve element when the solenoid is not excited, and to take in the fuel from a fuel inlet into a pressurizing chamber formed in the cylinder by retracting the plunger. After the solenoid is excited to close the valve element and the pressurizing chamber is closed, the plunger is extended to reduce the volume of the pressurizing chamber, thereby increasing the fuel pressure of the pressurizing chamber. As a result, by pushing a check valve of the discharge port provided in the cylinder, fuel is supplied to the in-cylinder injection injectors. When the valve element is opened, the fuel in the cylinder flows back to the intake side. By adjusting the closing timing of the valve element, it is possible to adjust the fuel pressure (fuel amount) to be supplied to the in-cylinder injection injectors.
When the electromagnetic spill valve is seated on a valve seat, vibration occurs. This vibration is transmitted to a rocker cover from the high-pressure pump and the rocker cover vibrates, thereby generating noise. Conventionally, in the intake passage injection mode for supplying fuel to only the intake passage, the closing timing of the electromagnetic spill valve is delayed to leave the electromagnetic spill valve in the open state when the plunger is extended, so that the fuel is returned to the suction port. As this is only delaying the closing timing of the valve element, the number of closing the valve element is not reduce and thus, the vibration and noise caused by the closing operation is not reduced.
During the idling operation of the internal combustion engine, operating noise of the internal combustion engine is small. Thus, the noise caused by the electromagnetic spill valve is relatively too large to ignore. Therefore, the measure to reduce the noise may be taken by stopping the fuel injection into the in-cylinder injection injectors in the idle operation, and injecting fuel from the intake passage injection injectors. However, there is a problem that, once the fuel injection from in-cylinder injection injectors is stopped, deposits are deposited in-cylinder injection injectors. Therefore, in Patent Reference 1, a fuel injection control means for solving these two problems is disclosed. This means is configured to perform the fuel injection control specific to each operation state of a cold idle state, a warm idle state and a high-temperature idle state that are partitioned according to the temperature of the internal combustion engine, mainly by in-cylinder injection or intake passage injection by the low-pressure pump without using the high-pressure pump.
In Patent Reference 2, a control means having the purpose that is similar to Patent Reference 1 is disclosed. This control means is equipped with a control unit which comprises a noise level estimation means for estimating a noise level in a compartment and a deposit estimation means for estimating whether or not it is in the operation state where deposits tend to accumulate in the in-cylinder injection injectors. When the noise level estimated by this control unit is below a set value, the pressurizing operation by the high-pressure pump is inhibited, whereas when the estimated noise level is not less than the set value and it is estimated that deposits tend to accumulate in the in-cylinder injection injectors, fuel is supplied from the low-pressure pump to the in-cylinder injection injectors without boosting the fuel.